This invention relates generally to compression springs and more particularly to a compression spring made from an elongate flat strip which is circularly coiled and formed with circular flat shim portions at opposite ends of the compression spring.
Crest-to-crest compression springs are coiled springs which are typically made from a flat metal strip and formed in a generally sinusoidal wave pattern. These springs are described as "crest-to-crest" because of the particular orientation of the individual spring turns in which the crest portions of the waves of one turn abut the trough portions of the waves in the turns immediately adjacent it.
In an ordinary crest-to-crest compression spring, an imbalance of the spring occurs due to the difficulty of arranging a completely symmetrical orientation of the crests (or troughs) of successive waves of the final spring turns at the opposite ends of the spring. The compression spring naturally tilts toward the point on its ends where the spring is lacking a wave crest portion to supply the required balance to the spring as a result of the helical format. Also, a continuous coiled spring naturally possesses a helical pitch at its spring ends which results in the lack of a support surface which is perpendicular to the spring longitudinal axis. This can cause an imbalance which becomes apparent when the spring is loaded, where the loading member rests on the wave crest portions of the last turn of the compression spring ends. Due to this imbalance, such compression springs can undergo uneven axial pressures when loaded. These uneven axial loads can cause the spring to exert opposite forces in both its radial and axial directions which detract from the designed load carrying ability of the spring, which is to exert a force only along the axial direction.
To minimize this imbalance problem, the compression spring designer must either increase the number of waves per spring turn to provide additional load support wave crest portions or decrease the amplitude of each wave of the entire spring to decrease the imbalance at the spring ends.
Other attempts to solve this imbalance problem have included using round wire for the compression spring in which the round wire at the opposite end portions of the compression spring are ground to form flat disc-like load support surfaces. However, this method is relatively expensive and time consuming, but it also requires a thick wire cross-section to provide a strong load support surface at the spring ends.
The present invention avoids the above-mentioned shortcomings. In a compression spring incorporating the principles of the present invention, a circular spring is formed from a flat, elongate wire strip into a continuous circular and substantially sinusoidal wavepath in which substantially all of the waves in the center turns of the compression spring have the same amplitude and wherein the waves in the spring turns adjacent the center turns have a diminishing amplitude which incrementally diminishes down to zero amplitude such that a portion of each of the last spring turns at opposite ends of the spring forms a flat circular shim end, which forms a plane generally perpendicular to the longitudinal axis of the spring.
Accordingly it a general object of the present invention to provide a new and improved spiral-wound compression spring having flat ends.
It is another object of the present invention to provide a multiturn crest-to-crest compression spring in which the compression spring has flat shim portions at opposite ends of the spring which provide uniform support surfaces for the spring which are substantially perpendicular to the longitudinal axis of the spring.
It is a further object of the present invention to provide a crest-to-crest spirally wound compression spring in which the crest and troughs of some of the waves diminish in amplitude down to zero such that flat circular shim ends are formed on opposite ends of the longitudinal axis of the compression spring.
It is yet a further object of the present invention to eliminate uneven axial and radial loading in a compression spring by incorporating balancing means in a compression spring by gradually tapering the heights of successive waves in certain successive spring turns to form a flat circular shim for the spring to rest on at its opposite ends, thereby providing the compression spring which exerts a force in only the axial direction when loaded under compression, eliminating the combination of radial and axial forces in the spring.
These and other objects features and advantages of the present invention will be clearly understood through a consideration of the following detailed description.